Angiogenesis may be defined as the development of a blood supply to a given area of tissue. The development of a blood supply may be part of normal embryonic development, represent the revascularization of a wound bed, or involve the stimulation of vessel growth by inflammatory or malignant cells. Sometimes angiogenesis is defined as the proliferation of new capillaries from pre-existing blood vessels. New growth of soft tissue requires new vascularization, and the concept of angiogenesis is a key component of tissue growth and in particular, a key point of intervention in pathological tissue growth.
Angiogenesis is a fundamental process necessary for embryonic development, subsequent growth, and tissue repair. Angiogenesis is a prerequisite for the development and differentiation of the vascular tree, as well as for a wide variety of fundamental physiological processes including embryogenesis, somatic growth, tissue and organ repair and regeneration, cyclical growth of the corpus luteum and endometrium, and development and differentiation of the nervous system. In the female reproductive system, angiogenesis occurs in the follicle during its development, in the corpus luteum following ovulation and in the placenta to establish and maintain pregnancy. Angiogenesis additionally occurs as part of the body's repair processes, e.g., in the healing of wounds and fractures.
Both controlled and uncontrolled angiogenesis are thought to proceed in a similar manner. Endothelial cells and pericytes, surrounded by a basement membrane, form capillary blood vessels. Angiogenesis begins with the erosion of the basement membrane by enzymes released by endothelial cells and leukocytes. The endothelial cells, which line the lumen of blood vessels, then protrude through the basement membrane. Angiogenic stimulants induce the endothelial cells to migrate through the eroded basement membrane. The migrating cells form a “sprout” off the parent blood vessel, where the endothelial cells undergo mitosis and proliferate. The endothelial sprouts merge with each other to form capillary loops, creating new blood vessels. Creation of the new microvascular system can initiate or exacerbate disease conditions.
Medical science has recognized that angiogenesis is an important factor in the initiation and/or proliferation of a large number of diverse disease conditions. Under normal physiological conditions, humans and other animals only undergo angiogenesis in very specific, restricted situations. For example, angiogenesis is normally observed in wound healing, fetal and embryonic development, and in the formation of the corpus luteum, endometrium and placenta. The process of angiogenesis has been found to be altered in a number of disease states, and in many instances, the pathological damage associated with the disease is related to uncontrolled angiogenesis. Since it was first put forward over thirty years ago, the hypothesis that angiogenesis is required for tumor growth and metastasis has gained extensive experimental support (Folkman, J. (1971) N. Engl. J. Med. 285, 1182-1186, Hanahan, D. & Folkman, J. (1996) Cell 86, 353-364). For example, angiogenesis is a factor in tumor growth, since a tumor must continuously stimulate growth of new capillary blood vessels in order to grow. Angiogenesis is an essential part of the growth of human solid cancer, and abnormal angiogenesis is associated with other diseases such as rheumatoid arthritis, psoriasis, and diabetic retinopathy (Folkman, J. and Klagsbrun, M., Science 235:442-447,(1987)). In addition to tumor growth and metastasis, angiogenesis has also been implicated in rheumatoid arthritis, diabetic retinopathy and macular degeneration, suggesting that inhibition of angiogenesis may be useful for the treatment of these disorders (Carmeliet, P. (2003) Nat. Med. 9, 653-660).
One way to accelerate the drug discovery process for angiogenesis related disorders/diseases involves finding new uses for existing drugs. Because the toxicity, pharmacokinetics, and clinical properties of existing drugs are well established, compounds that show activity can be rapidly and inexpensively evaluated as new treatments and moved into the clinic if appropriate. Furthermore, the extensive structure/activity data accumulated during the development of each drug can greatly facilitate mechanistic studies for target identification or validation.
Clearly, the development and progress of many disease conditions can be controlled by controlling the process of angiogenesis. However, many materials which appear promising in vitro have proven to be relatively ineffective when applied in vivo. Furthermore, various of such materials have been found to be unstable, toxic, or otherwise difficult to employ. Consequently, there is a need for methods and materials capable of controlling and inhibiting angiogenesis in a reliable manner. It is therefore an object of the invention to provide compounds and pharmaceutical compositions which exhibit activity as inhibitors of angiogenesis.